1. Field of the Invention
The invention relates to a process for the production of shaped structures of cellulose with the aid of cellulose derivatives.
2. Description of the Related Art
The use of cellulose derivatives for the production of cellulosic fibers is known. Cellulose xanthogenates are usually employed, and are spun in alkaline solution and regenerated to cellulose with strong acids. This process is described, for example, in: Dr. K. Gotze, "Chamie-fasern nach dem Viskoseverfahren (Synthetic Fibers by the Viscose Process)", Springer Verlag 1967.
The disadvantages of this process are the formation of large amounts of by-products, such as sodium sulfate and hydrogen sulfide.
It has also been proposed to replace the sulfur derivatives by nitrogen derivatives. A carbamate process is described, for example, by O. T. Turunen, J. Fors and J. I. Huttunen in Lenzinger Ber. 59 (1985), page 111. The disadvantage of this process also is the large amount of sodium sulfate obtained.
Processes furthermore are known for the production of cellulosic fibers in which cellulose acetate fibers (2,5- or 3-acetates) spun from organic solvents are then hydrolyzed. Examples of these are to be found in U.S. Pat. No. 4,464,323.
The disadvantage of this process is the large amount of sodium acetate obtained.
The preparation, properties and uses of highly hydrolyzed cellulose acetates are described in Industrial and Engineering Chemistry, 49(1), pages 79-83 (1957). Regeneration of such derivatives to cellulose is not disclosed.
A dry spinning process for cellulose fibers is known from U.S. Pat. No. 3,482,011. Spinning is carried out from mixtures comprising water-miscible solvents. Spinning from water leads to problems. Regeneration of the resulting fibers to cellulose is not disclosed.
U.S. Pat. No. 4,983,730 describes cellulose acetate mixtures of components of various molecular weights and the production of fibers from such mixtures. A dry spinning process is not disclosed.
A novel process for the production of cellulosic fibers is based on the direct solution of cellulose in N-methylmorpholine N-oxide and a subsequent wet spinning process. Such a process is described, for example, in EP-A-0 490 870. The disadvantage of this process is that solvent residues remain in the fiber and can cause trouble, for example, during use in medical or hygiene sectors.
There is thus still a need for a process for the production of shaped structures of cellulose in which low amounts of by-products are formed, in particular for a process which operates without the formation of large amounts of by-product and in which, in particular, no organic solvent is employed.